cgroup: Remove data-race around cgrp_dfl_visible

There's a seemingly harmless data-race around cgrp_dfl_visible detected by
kernel concurrency sanitizer. Let's remove it by throwing WRITE/READ_ONCE at
it.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Abhishek Shah <abhishek.shah@columbia.edu>
Cc: Gabriel Ryan <gabe@cs.columbia.edu>
Reviewed-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Link: https://lore.kernel.org/netdev/20220819072256.fn7ctciefy4fc4cu@wittgenstein/

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 0005de2..e0b72eb 100644 (file)
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -2173,7 +2173,7 @@ static int cgroup_get_tree(struct fs_context *fc)
        struct cgroup_fs_context *ctx = cgroup_fc2context(fc);
        int ret;
 
-       cgrp_dfl_visible = true;
+       WRITE_ONCE(cgrp_dfl_visible, true);
        cgroup_get_live(&cgrp_dfl_root.cgrp);
        ctx->root = &cgrp_dfl_root;
 
@@ -6098,7 +6098,7 @@ int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
                struct cgroup *cgrp;
                int ssid, count = 0;
 
-               if (root == &cgrp_dfl_root && !cgrp_dfl_visible)
+               if (root == &cgrp_dfl_root && !READ_ONCE(cgrp_dfl_visible))
                        continue;
 
                seq_printf(m, "%d:", root->hierarchy_id);